1. Technical Field
The present invention relates to a lithography mask or reticle, and more particularly relates to a reflective mask or reticle.
2. Background
Advancements in photolithography technology allow semiconductor integrated circuits to be produced in smaller and smaller sizes and with better and better performance. Deep ultra-violet (DUV) light with a wavelength of 248, 193, or 157 nanometers has recently been applied to chip manufacturing. Several candidate methods, based on extreme ultraviolet (EUV) light, x-rays, electrons, and ion beams, are competing to emerge as the next generation of lithography techniques.
EUV lithography (EUVL) is probably the most promising candidate and uses EUV light with a wavelength of about 10 to 15 nanometers. EUVL uses reflective rather than refractive optics for wafer exposure owing to a lack of availability of EUV transparent materials. EUV light may be generated using discharge-produced plasma (DPP), and the generated EUV light may be directed by a series of Bragg mirrors to a reflective mask used to pattern a photoresist on a wafer. The entire exposure process is conducted in vacuum conditions to prevent the absorption of the UV light by the air.
To date, developing a suitable quality EUVL mask is the top challenge in EUVL technology. EUVL mask technologies consist of EUVL blank mask preparation and mask fabrication from raw stock. Blank mask preparation requires a flat and defect-free substrate with an extremely low coefficient of thermal expansion and a defect-free multi-layer with accurate thickness and chemical composition. Stringent EUV mask specifications are difficult to meet and result in significantly high EUV mask cost.